Spin-injection magnetic random access memory

ABSTRACT

A spin-injection magnetic random access memory according to an embodiment of the invention includes a magnetoresistive element having a magnetic fixed layer whose magnetization direction is fixed, a magnetic recording layer whose magnetization direction can be changed by injecting spin-polarized electrons, and a tunnel barrier layer provided between the magnetic fixed layer and the magnetic recording layer, a bit line which passes spin-injection current through the magnetoresistive element, the spin-injection current being used for generation of the spin-polarized electrons, a writing word line through which assist current is passed, the assist current being used for the generation of an assist magnetic field in a magnetization easy-axis direction of the magnetoresistive element, and a driver/sinker which determines a direction of the spin-injection current and a direction of the assist current.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of, and claims thebenefit of priority under 35 U.S.C. § 120 from, U.S. application Ser.No. 11/242,906, filed Oct. 5, 2005, which claims the benefit of priorityunder 35 U.S.C. § 119 from Japanese patent application No. 2005-021877,filed Jan. 28, 2005. The entire contents of each of the aboveapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a spin-injection magnetic random accessmemory in which magnetization reversal is performed with spin-polarizedelectrons.

2. Description of the Related Art

In addition to magnetic heads and detection elements such as a magneticsensor, a magnetoresistive element in which a magnetic film is used hasbeen studied for the use of a storage element in a magnetic randomaccess memory (MRAM), which is of a solid-state magnetic memory.

The magnetoresistive element has a sandwich structure, which includes,e.g., two magnetic metal layers and a dielectric layer arranged therebetween. In the magnetoresistive element having the sandwich structure,because magnetization states of the two magnetic metal layers differdepending on the data, the data can be read by utilizing tunnelingmagnetoresistance (TMR) effect.

Recently, for an MR ratio (magnetoresistive ratio), which indicates amagnetoresistive fluctuation rate, the magnetoresistive element havingthe MR ratios more than 20% at room temperature is obtained, andresearch and development of the magnetic random access memory isactively conducted.

The magnetoresistive element in which the TMR effect is utilized can berealized as follows: After an Al (aluminum) layer having thicknessesranging from 0.6 nm to 2.0 nm is formed on a ferromagnetic body which isof the magnetic metal layer, a surface of the Al layer is exposed tooxygen glow discharge or oxygen gas to form a tunnel barrier layer madeof Al₂O₃, and the ferromagnetic body which is of the magnetic metallayer is further formed.

Instead of Al₂O₃, MgO (magnesium oxide) can also be used as the tunnelbarrier layer.

A ferromagnetic single-tunnel junction element is proposed as anotherstructure of the magnetoresistive element in which the TMR effect isutilized. In the ferromagnetic single-tunnel junction element, forexample, one of two ferromagnetic layers is formed in a magnetic fixedlayer whose magnetization state is fixed by an anti-ferromagnetic layer.Further, a magnetoresistive element, which has a ferromagnetic tunneljunction through magnetic particles dispersed in a dielectric body and aferromagnetic double-tunnel junction element in which the ferromagneticbody is formed in a continuous film are also proposed.

These magnetoresistive elements have been considered to have a highpotential for application, because the MR ratios range from 20% to 230%and a decrease in MR ratio is suppressed even if voltage applied to themagnetoresistive element is increased.

In the magnetic random access memory in which the magnetoresistiveelement is used, a readout time is as fast as not more than 10 nanoseconds and rewritable endurance is as large as at least 10¹⁵ times.

However, the data writing (magnetization reversal) in the magneticrecording layer is performed with a magnetic field generated by pulsecurrent. Therefore, current density of the pulse current supplied to aword line or a bit line is increased, which results in new problems thatelectric power consumption is increased, large memory capacity isdifficult to be realized, and a driver for generating the pulse currentis increased in an area.

Therefore, there is proposed a yoke wiring technology in which amagnetic material (yoke material) having high magnetic permeability isprovided around a writing line to impart efficiently the magnetic fieldto the magnetoresistive element. According to this technology, thecurrent density of the pulse current generated during the data writingcan be decreased.

However, the pulse current cannot still be decreased to a value requiredfor the practical use of the magnetic random access memory, i.e., thevalues not more than 1 mA.

The writing method by the spin injection is proposed as the technology,which solves these problems at a stroke.

The spin-injection writing method has a feature in that themagnetization reversal of the magnetic recording layer is performed byinjecting the spin-polarized electrons into the magnetic recording layerof the magnetoresistive element.

When the magnetization reversal is performed by the spin-polarizedelectrons, because the current density of the pulse current can bedecreased compared with the case in which the magnetization reversal isperformed by the magnetic field, the spin-injection writing method cancontribute to the electric power consumption reduction, the enlargementof memory capacity, the driver area reduction, and the like. In thiscase, in order not to generate the ring magnetic field by the pulsecurrent, because it is necessary to decrease dimensions of themagnetoresistive element, it is convenient to integrate themagnetoresistive element.

In order to realize the spin-injection writing method, firstly, it isnecessary that thermal stability (thermal fluctuation resistance) isensured when the dimensions of the magnetoresistive element is equal toor smaller than 0.1×0.1 μm2. Second it is necessary that a fluctuationin dimension of the magnetoresistive element is decreased. Third it isnecessary that the current density of the pulse current required for thespin-injection magnetization reversal is decreased.

Currently the current density of the pulse current required for thespin-injection magnetization reversal is about 10⁷ A/cm², however, thefurther reduction of the current density is desired in order to preventa tunnel barrier breakage problem and the like.

In the magnetoresistive element in which giant magnetoresistance (GMR)effect is utilized, the current density of the pulse current can bedecreased to a degree of 10⁶ A/cm² by adopting the so-called dual-pinstructure. For example, in the case where Cu/CO₉₀Fe₁₀, Ru/Co₉₀Fe₁₀ isused as a spin reflection film, the current densities of the pulsecurrent required for the spin-injection magnetization reversal becomeabout 8×10⁶ A/cm² and about 2×10⁶ A/cm² respectively.

However, these values are not still enough to realize the magneticrandom access memory. In order to solve the problems such as the tunnelbarrier breakage and the thermal disturbance caused by the temperaturerise of the magnetoresistive element, it is necessary to conduct theresearch and development of a new architecture and writing method, whichcan realize the further reduction of the current density.

SUMMARY OF THE INVENTION

A spin-injection magnetic random access memory according to one aspectof the present invention comprises: a magnetoresistive element having amagnetic fixed layer whose magnetization direction is fixed, a magneticrecording layer whose magnetization direction can be changed byinjecting spin-polarized electrons, and a tunnel barrier layer which isprovided between the magnetic fixed layer and the magnetic recordinglayer; a bit line which passes spin-injection current through themagnetoresistive element, the spin-injection current being used forgeneration of the spin-polarized electrons; a writing word line throughwhich assist current is passed, the assist current being used for thegeneration of an assist magnetic field in a magnetization easy-axisdirection of the magnetoresistive element; a first driver/sinker whichis connected to the bit line; a second driver/sinker which is connectedto the writing word line; a first decoder which controls the firstdriver/sinker to determine a direction of the spin-injection currentaccording to a value of writing data in writing data in themagnetoresistive element while determining timing of cutoff of thespin-injection current; and a second decoder which controls the seconddriver/sinker to determine the direction of the spin-injection currentaccording to the value of the writing data during the data writing whilemaking the timing of the cutoff of the assist current later than thetiming of the cutoff of the spin-injection current.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows thermal disturbance of a magnetoresistive element;

FIG. 2 shows temperature rise of the magnetoresistive element duringspin-injection writing;

FIG. 3 is a sectional view showing a first embodiment of a structure;

FIG. 4 is a sectional view showing the first embodiment of thestructure;

FIG. 5 is a sectional view showing the first embodiment of thestructure;

FIG. 6 is a sectional view showing the first embodiment of thestructure;

FIG. 7 is a sectional view showing a second embodiment of the structure;

FIG. 8 is a sectional view showing the second embodiment of thestructure;

FIG. 9 is a sectional view showing the second embodiment of thestructure;

FIG. 10 is a sectional view showing the second embodiment of thestructure;

FIG. 11 is a sectional view showing a first embodiment of amagnetoresistive element;

FIG. 12 is a sectional view showing a second embodiment of themagnetoresistive element;

FIG. 13 is a sectional view showing a third embodiment of themagnetoresistive element;

FIG. 14 is a sectional view showing a fourth embodiment of themagnetoresistive element;

FIG. 15 is a sectional view showing a fifth embodiment of themagnetoresistive element;

FIG. 16 is a sectional view showing the fifth embodiment of themagnetoresistive element;

FIG. 17 is a sectional view showing the fifth embodiment of themagnetoresistive element;

FIG. 18 is a sectional view showing the fifth embodiment of themagnetoresistive element;

FIG. 19 shows a flowchart of a writing method according to Example ofthe invention;

FIG. 20 is a waveform chart showing on/off timing of a spin-injectioncurrent and an assist magnetic field;

FIG. 21 is a circuit diagram showing a peripheral circuit of a magneticrandom access memory according to an embodiment of the invention;

FIG. 22 is a waveform chart showing a waveform of a signal used for thememory of FIG. 21;

FIG. 23 shows an example of a decoder;

FIG. 24 shows the example of the decoder;

FIG. 25 shows the example of the decoder;

FIG. 26 shows the example of the decoder;

FIG. 27 shows the example of the decoder;

FIG. 28 shows an example of an active signal RWL generating circuit;

FIG. 29 shows an example of an active signal E2W generating circuit;

FIG. 30 shows an example of an active signal W2E generating circuit;

FIG. 31 shows an example of an active signal N2S generating circuit;

FIG. 32 shows an example of an active signal S2N generating circuit;

FIG. 33 shows an example of a circuit, which determines timing of anactive signal;

FIG. 34 shows the example of the circuit, which determines the timing ofthe active signal;

FIG. 35 is a waveform chart showing signals outputted from the circuitsof FIGS. 33 and 34;

FIG. 36 shows an example of a delay circuit;

FIG. 37 shows the example of the delay circuit;

FIG. 38 is a sectional view showing a modification of the firstembodiment of the structure;

FIG. 39 is a sectional view showing the modification of the firstembodiment of the structure;

FIG. 40 is a sectional view showing the modification of the firstembodiment of the structure;

FIG. 41 is a sectional view showing the modification of the firstembodiment of the structure;

FIG. 42 is a sectional view showing a modification of the secondembodiment of the structure;

FIG. 43 is a sectional view showing the modification of the secondembodiment of the structure;

FIG. 44 is a sectional view showing the modification of the secondembodiment of the structure;

FIG. 45 is a sectional view showing the modification of the secondembodiment of the structure;

FIG. 46 shows the thermal disturbance of the magnetoresistive element;

FIG. 47 shows the thermal disturbance of the magnetoresistive element;

FIG. 48 shows the thermal disturbance of the magnetoresistive element;and

FIG. 49 shows the thermal disturbance of the magnetoresistive element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A spin-injection magnetic random access memory of an aspect of thepresent invention will be described below in detail with reference tothe accompanying drawings.

1. ARCHITECTURE AND WRITING METHOD

(1) Thermal Disturbance

FIG. 1 shows the thermal disturbance of the conventionalmagnetoresistive element.

It is assumed that the magnetization reversal by the spin injection isperformed with the pulse current (spin-polarized electrons) having apulse width of 50 ns.

When the magnetization reversal (switching) is performed by supplyingthe pulse current to a magnetoresistive element MTJ, a fluctuation incurrent density (corresponding to pulse voltage) of the pulse currentrequired for the switching and a fluctuation in magnetoresistivefluctuation rate (corresponding to junction resistance) ofpost-switching are generated in each writing.

It is thought that the fluctuations are caused by the pulse currentsupplied to the magnetoresistive element MTJ during the switching. Thatis, the pulse current causes temperature rise of the magnetoresistiveelement MTJ. It is believed that the temperature rise of themagnetoresistive element MTJ has some effects on the magnetic recordinglayer (free layer) during the switching.

FIG. 2 shows the temperature rise of the magnetoresistive element whenthe magnetization reversal is performed with the pulse current havingthe pulse width of 50 ns.

While the pulse current is supplied to the magnetoresistive element, thetemperature of the magnetoresistive element is increased at a constantrate. The temperature is increased up to 130° C. After the pulse currentis cut off, it takes tens nanoseconds to sufficiently cool themagnetoresistive element. For example, in the embodiments, it takes atleast 50 ns to sufficiently cool the magnetoresistive element.

(2) Structure

In embodiments of the invention, the magnetic field in a magnetizationeasy-axis direction of the magnetoresistive element is used as assistfor the magnetization reversal (switching) in the spin-injectionmagnetic random access memory in which the magnetization reversal isperformed by the spin-polarized electrons.

That is, in the spin-injection magnetization reversal method, althoughthe recording layer is largely affected by the thermal fluctuationbecause the magnetization reversal is performed by encouraging electronspin precession, the assist magnetic field suppresses the thermaldisturbance by the electron spin in the recording layer until thetemperature of the magnetoresistive element which rises due to thespin-polarized electrons sufficiently falls down.

Thus, when the assist magnetic field is imparted during themagnetization reversal with the spin-polarized electrons, the electronspin precession is suppressed to decrease the fluctuation incharacteristics of the magnetoresistive element due to the thermaldisturbance.

Further, the assist magnetic field decreases the current density of thepulse current used for the spin-injection magnetization reversal, whichallows the problems such as the tunnel barrier breakage to be prevented.

The assist magnetic field in the magnetization easy axis direction ofthe magnetoresistive element does not mainly perform the magnetizationreversal, but suppress the electron spin thermal disturbance in the freelayer during the switching, so that assist currents not more than 1 mAare enough to generate the assist magnetic field. It should also benoted that the magnetization reversal is not performed only by theassist magnetic field.

(i) First Embodiment

FIGS. 3 to 6 show a first embodiment of the structure.

A memory cell includes one MOS transistor Tr and one magnetoresistiveelement MTJ.

One end of the magnetoresistive element MTJ is connected to a bit lineBLu, and the other end is connected to a bit line BLd through the MOStransistor TR, which is of a selection element. The two bit lines BLuand BLd are arranged so as to intersect each other.

In the embodiment, the bit line BLu extends in a magnetization hard-axisdirection of the magnetoresistive element MTJ, and the bit line BLdextends in a magnetization easy-axis direction of the magnetoresistiveelement MTJ. However, the opposite is true.

The two bit lines BLu and BLd may be arranged in parallel with eachother.

A spin-injection current (pulse current) Is for generating thespin-injection magnetization reversal is supplied to themagnetoresistive element MTJ during the data writing.

For example, when the spin-injection current Is is supplied from bitline BLu toward the bit line BLd, the magnetization direction of therecording layer is directed to the same direction as that of the fixedlayer (pinned layer) (parallel state). When the spin-injection currentIs is supplied from bit line BLd toward the bit line BLu, themagnetization direction of the recording layer is directed to theopposite direction to that of the fixed layer (anti-parallel state).

At this point, in the embodiment, a writing word line WWL extending inthe magnetization hard-axis direction is arranged near themagnetoresistive element MTJ.

An assist current (pulse current) Ia is passed through the writing wordline WWL during the data writing, and the assist current (pulse current)Ia has the direction according to a value of the writing data. Theassist current Ia generates an assist magnetic field H in themagnetization easy-axis direction, in which the assist magnetic field Hsuppresses the electron spin thermal disturbance in the recording layerof the magnetoresistive element MTJ.

Referring to FIG. 3, the writing word line WWL is arranged above themagnetoresistive element MTJ, and the writing word line WWL extends inthe same direction as the bit line BLu. Referring to FIG. 4, the writingword line WWL is arranged above the magnetoresistive element MTJ, andthe writing word line WWL extends in the direction intersecting the bitline BLu.

Referring to FIG. 5, the writing word line WWL is arranged below themagnetoresistive element MTJ, and the writing word line WWL extends inthe same direction as the bit line BLu. Referring to FIG. 6, the writingword line WWL is arranged below the magnetoresistive element MTJ, andthe writing word line WWL extends in the direction intersecting the bitline BLu.

As described above, the temperature of the magnetoresistive element MTJis held at a high level for tens nanoseconds even after thespin-injection current Is is cut off. Because the assist magnetic fieldH is used in order to suppress the electron spin thermal disturbance inthe recording layer, the passage of the assist current Ia is continuedfor tens nanoseconds after the spin-injection current Is is cut off.

Timing in which the assist current 1 a is passed may be set at the sametiming in which the spin-injection current Is is passed, or the timingin which the assist current Ia is passed may be earlier or later thanthe timing in which the spin-injection current Is is passed.

(ii) Second Embodiment

FIGS. 7 to 10 show a second embodiment of the structure.

As with the first embodiment, the memory cell includes one MOStransistor Tr and one magnetoresistive element MTJ.

The second embodiment differs from the first embodiment in that themagnetoresistive element MTJ is an edge type tunnel magnetoresistiveelement.

While the tunnel barrier layer is formed on the upper surface of thefixed layer as shown in FIGS. 3 to 7 in the normal magnetoresistiveelement, the tunnel barrier layer is formed on a side face (board lineportion) of the fixed layer in the edge type tunnel magnetoresistiveelement. Therefore, a junction area between the fixed layer and thetunnel barrier layer can be determined by the thickness of the fixedlayer, which allows the fluctuation in characteristics among theelements to be decreased.

As with the first embodiment, the spin-injection current Is forgenerating the spin-injection magnetization reversal is supplied to themagnetoresistive element MTJ during the data writing.

For example, when the spin-injection current Is is supplied from bitline BLu toward the bit line BLd, the magnetization direction of therecording layer is directed to the same direction as that of the fixedlayer (parallel state). When the spin-injection current Is is suppliedfrom bit line BLd toward the bit line BLu, the magnetization directionof the recording layer is directed to the opposite direction to that ofthe fixed layer (anti-parallel state).

An assist current Ia is passed through the writing word line WWL duringthe data writing and the assist current (pulse current) Ia has thedirection according to a value of the writing data. The assist currentIa generates the assist magnetic field H in the magnetization easy-axisdirection and the assist magnetic field H suppresses the electron spinthermal disturbance in the recording layer of the magnetoresistiveelement MTJ.

Referring to FIG. 7, the writing word line WWL is arranged above themagnetoresistive element MTJ, and the writing word line WWL extends inthe same direction as the bit line BLu. Referring to FIG. 8, the writingword line WWL is arranged above the magnetoresistive element MTJ, andthe writing word line WWL extends in the direction intersecting the bitline BLu.

Referring to FIG. 9, the writing word line WWL is arranged below themagnetoresistive element MTJ, and the writing word line WWL extends inthe same direction as the bit line BLu. Referring to FIG. 10, thewriting word line WWL is arranged below the magnetoresistive elementMTJ, and the writing word line WWL extends in the direction intersectingthe bit line BLu.

As with the first embodiment, the timing in which the assist current Iais passed may be set at the same timing in which the spin-injectioncurrent Is is passed, or the timing in which the assist current Ia ispassed may be earlier or later than the timing in which thespin-injection current Is is passed.

As with the first embodiment, the timing in which the assist current Iais cut off is set at the time when tens nanoseconds elapses since thespin-injection current Is is cut off.

(3) Structure of Magnetoresistive Element

In order to realize the large-capacity spin-injection magnetic randomaccess memory by solving the problems such as the tunnel barrierbreakage and the thermal disturbance by the temperature rise of themagnetoresistive element, it is necessary that the structure of themagnetoresistive element is also studied.

It is necessary that the magnetoresistive element can be provided forthe spin-injection magnetization reversal and can perform themagnetization reversal at low current density. Some embodiments for itwill be described below.

(i) First Embodiment

FIG. 11 shows a first embodiment of the magnetoresistive element.

In the first embodiment, the magnetoresistive element includes ananti-ferromagnetic layer 3, a first magnetic fixed layer 4, a tunnelbarrier layer 5, a magnetic recording layer 6, a non-magnetic metallayer 7, a second magnetic fixed layer 8, and an anti-ferromagneticlayer 9. The magnetic recording layer 6 is arranged on the firstmagnetic fixed layer 4 through tunnel barrier layer 5. The secondmagnetic fixed layer 8 is arranged on the magnetic recording layer 6through the non-magnetic metal layer 7.

In the first magnetic fixed layer 4, the magnetization state is fixed byexchange interaction bonding between the first magnetic fixed layer 4and the anti-ferromagnetic layer 3. In the second magnetic fixed layer8, the magnetization state is fixed by the exchange interaction bondingbetween the second magnetic fixed layer 8 and the anti-ferromagneticlayer 9. The magnetization direction of the first magnetic fixed layer 4is set in the opposite direction to the magnetization direction of thesecond magnetic fixed layer 8.

The magnetoresistive element is arranged on a ground layer 2 which is ofan electrode, and an electrode layer 10 is arranged on theanti-ferromagnetic layer 9.

When the spin-injection current is passed from the electrode layer 10 tothe ground layer 2, the spin-polarized electrons are injected from thefirst magnetic fixed layer 4 into the magnetic recording layer 6, andthe magnetization direction of the magnetic recording layer 6 becomes asame direction of the first magnetic fixed layer 4 (parallel state).When the spin-injection current is passed from the ground layer 2 to theelectrode layer 10, the spin-polarized electrons are injected from thesecond magnetic fixed layer 8 into the magnetic recording layer 6, andthe magnetization direction of the magnetic recording layer 6 becomes ina same direction of the second magnetic fixed layer 8 (anti-parallelstate).

In the spin-injection magnetization reversal method, in order toefficiently perform the magnetization reversal, the non-magnetic metallayer 7 and the second magnetic fixed layer 8 are formed by combinationof materials in which spin reflectivity is enhanced.

For example, in the case where the second magnetic fixed layer 8 is madeof the ferromagnetic material including Co (for example, Co rich), thenon-magnetic metal layer 7 is made of at least one metal selected fromthe group of Zr, Hf, Rh, Ag, Cu, and Au, preferably from the group ofZr, Hf, Rh, and Ag or an alloy including at least one metal thereof.

Additionally, in the case where the second magnetic fixed layer 8 ismade of the ferromagnetic material including Fe (for example, Fe rich),the non-magnetic metal layer 7 is made of at least one metal selectedfrom the group of Rh, Pt, Ir, Al, Ga, Cu, and Au, preferably from thegroup of Rh, Pt, Ir, Al, and Ga or the alloy including at least onemetal thereof.

In the case where the second magnetic fixed layer 8 is made of theferromagnetic material including Ni (for example, Ni rich), thenon-magnetic metal layer 7 is made of at least one metal selected fromthe group of Zr, Hf, Au, Ag, and Cu, preferably from the group of Zr,Hf, Au, and Ag or the alloy including at least one metal thereof.

According to the above structure, the second magnetic fixed layer 8reflects the electron, which is spin-polarized in the opposite directionto the magnetization direction (direction of electron spin) of thesecond magnetic fixed layer 8. Therefore, the proper selection of thematerial for the non-magnetic metal layer 7 enables the efficientreflection of the electrons, spin-polarized in the opposite direction tothe magnetization direction of the second magnetic fixed layer 8, toreverse the magnetization state of the magnetic recording layer 6.

It is necessary that the magnetic moment directions of the firstmagnetic fixed layer 4 and the second magnetic fixed layer 8 alwaysdiffer from each other by about 180 degrees.

Therefore, for example, the anti-ferromagnetic layers 3 and 9 havingdifferent Neel temperatures T_(N) may be added to the first magneticfixed layer 4 and the second magnetic fixed layer 8 respectively, andthe direction of the magnetic field can be reversed by 180 degrees whenthe temperature is between the Neel temperatures T_(N) during thecooling in the annealing process of determining the magnetizationdirection.

(ii) Second Embodiment

FIG. 12 shows a second embodiment of the magnetoresistive element.

The second embodiment is one of modifications of the first embodiment,and the second embodiment differs from the first embodiment in thestructure of the second magnetic fixed layer.

In the second embodiment, the magnetoresistive element includes theanti-ferromagnetic layer 3, the first magnetic fixed layer 4, the tunnelbarrier layer 5, the magnetic recording layer 6, the non-magnetic metallayer 7, a second magnetic fixed layer 8SAF, and the anti-ferromagneticlayer 9. The magnetic recording layer 6 is arranged on the firstmagnetic fixed layer 4 through tunnel barrier layer 5. The secondmagnetic fixed layer 8SAF and the anti-ferromagnetic layer 9 arearranged on the magnetic recording layer 6 through the non-magneticmetal layer 7.

In the first magnetic fixed layer 4, the magnetization state is fixed bythe exchange interaction bonding between the first magnetic fixed layer4 and the anti-ferromagnetic layer 3. The second magnetic fixed layer8SAF has an SAF (Synthetic Anti-ferromagnetic) structure, and themagnetization state of the second magnetic fixed layer 8SAF is fixed.The adoption of the SAF structure can set the magnetization directionsof the first magnetic fixed layer 4 and the ferromagnetic layer, locatedon the tunnel barrier layer 5 side of the second magnetic fixed layer8SAF, at angles of 180 degrees in mutually opposite directions evenwithout using the annealing process required for the structure of thefirst embodiment.

In the second embodiment, when the electrons are injected from the firstmagnetic fixed layer 4 to the magnetic recording layer 6 in reversingthe magnetic moments (magnetization) between the first magnetic fixedlayer 4 and the magnetic recording layer 6 from the anti-parallel stateto the parallel state, the electrons spin-polarized in the firstmagnetic fixed layer 4 pass through the tunnel barrier layer 5 to impartspin torque to the magnetic recording layer 6.

The spin-polarized electrons reach the second magnetic fixed layer 8SAFfrom the magnetic recording layer 6 through the non-magnetic metal layer7. However, the spin-polarized electrons are reflected on the secondmagnetic fixed layer 8SAF, and the spin-polarized electrons, which areof the reflected spin electrons impart the spin torque to the magneticrecording layer 6 again.

Accordingly, when the magnetic moments between the first magnetic fixedlayer 4 and the magnetic recording layer 6 are in the anti-parallelstate, the magnetic moment of the magnetic recording layer 6 isreversed, and the magnetic moments between the first magnetic fixedlayer 4 and the magnetic recording layer 6 become in a parallel state.

When the electrons are injected from the second magnetic fixed layer8SAF to the magnetic recording layer 6 in reversing the magnetic moments(magnetization) between the first magnetic fixed layer 4 and themagnetic recording layer 6 from the parallel state to the anti-parallelstate, the electrons spin-polarized in the second magnetic fixed layer8SAF pass through the non-magnetic metal layer 7 to impart the spintorque to the magnetic recording layer 6.

The spin-polarized electrons tend to flow from the magnetic recordinglayer 6 to the first magnetic fixed layer 4 through the tunnel barrierlayer 5. However, because tunneling probability is lowered in theelectrons having the spins in the opposite direction to the magneticmoment of the first magnetic fixed layer 4 when the electrons is passedthrough the tunnel barrier layer 5, the electrons are reflected, and theelectrons which are of the reflected spin electrons impart the spintorque to the magnetic recording layer 6 again.

Accordingly, when the magnetic moments between the first magnetic fixedlayer 4 and the magnetic recording layer 6 are in the parallel state,the magnetic moment of the magnetic recording layer 6 is reversed, andthe magnetic moments between the first magnetic fixed layer 4 and themagnetic recording layer 6 become in an anti-parallel state.

Thus, the magnetization direction of the magnetic recording layer 6 canbe reversed by changing the passage direction of the spin-injectioncurrent, so that the writing of “0” and “1” can be performed by the spininjection.

In the case where the second magnetic fixed layer 8SAF is made of theferromagnetic material including Co (for example, Co rich), thenon-magnetic metal layer 7 is made of at least one metal selected fromthe group of Zr, Hf, Rh, Ag, Cu, and Au, preferably from the group ofZr, Hf, Rh, and Ag or an alloy including at least one metal thereof.

In the case where the second magnetic fixed layer 8SAF is made of theferromagnetic material including Fe (for example, Fe rich), thenon-magnetic metal layer 7 is made of at least one metal selected fromthe group of Rh, Pt, Ir, Al, Ga, Cu, and Au, preferably from the groupof Rh, Pt, Ir, Al, and Ga or the alloy including at least one metalthereof.

Furthermore, in the case where the second magnetic fixed layer 8SAF ismade of the ferromagnetic material including Ni (for example, Ni rich),the non-magnetic metal layer 7 is made of at least one metal selectedfrom the group of Zr, Hf, Au, Ag, and Cu, preferably from the group ofZr, Hf, Au, and Ag or the alloy including at least one metal thereof.

(iii) Third Embodiment

FIG. 13 shows a third embodiment of the magnetoresistive element.

In the third embodiment, the magnetoresistive element includes theanti-ferromagnetic layer 3, the first magnetic fixed layer 4, the tunnelbarrier layer 5, the magnetic recording layer 6, the non-magnetic metallayer 7, the second magnetic fixed layer 8, and the anti-ferromagneticlayer 9. The magnetic recording layer 6 is arranged on the firstmagnetic fixed layer 4 through tunnel barrier layer 5. The secondmagnetic fixed layer 8 is arranged on the magnetic recording layer 6through the non-magnetic metal layer 7.

In the first magnetic fixed layer 4, the magnetization state is fixed bythe exchange interaction bonding between the first magnetic fixed layer4 and the anti-ferromagnetic layer 3. In the second magnetic fixed layer8, the magnetization state is fixed by the exchange interaction bondingbetween the second magnetic fixed layer 8 and the anti-ferromagneticlayer 9. The magnetization direction of the first magnetic fixed layer 4is set in the same direction as the magnetization direction of thesecond magnetic fixed layer 8.

The magnetoresistive element is arranged on the ground layer 2, and theelectrode layer 10 is arranged on the anti-ferromagnetic layer 9.

In this configuration, when the spin-injection current is passed fromthe electrode layer 10 to the ground layer 2, the electrons are injectedfrom the first magnetic fixed layer 4 into the magnetic recording layer6, and the electrons spin-polarized in the same direction as themagnetic moment of the first magnetic fixed layer 4 in the firstmagnetic fixed layer 4 impart the spin torque to the magnetic recordinglayer 6 through the tunnel barrier layer 5 (parallel state). Further,the electrons are injected to the second magnetic fixed layer 8 throughthe magnetic recording layer 6 and the non-magnetic metal layer 7. Whenthe material for the non-magnetic metal layer 7 is selected, theelectrons having the spin in the same direction as the magnetic momentof the second magnetic fixed layer 8 are reflected on the secondmagnetic fixed layer 8 and injected again to the magnetic recordinglayer 6 as the reflected spin electron, which allows the magnetizationdirection of the magnetic recording layer 6 to be directed to the samedirection as that of the first magnetic fixed layer 4 (parallel state).

When the spin-injection current is passed from the ground layer 2 to theelectrode layer 10, the electrons are injected from the second magneticfixed layer 8 into the magnetic recording layer 6 through thenon-magnetic metal layer 7. When the material for the non magnetic metallayer 7 is selected, the electrons having the spin in the oppositedirection to the magnetic moment of the second magnetic fixed layer 8become dominant in passing the electrons spin-polarized in the secondmagnetic fixed layer 8 through the non-magnetic metal layer 7, and thespin-polarized electrons impart the spin torque to the magneticrecording layer 6. Further, the electrons tend to flow from the magneticrecording layer 6 to the first magnetic fixed layer 4 through the tunnelbarrier layer 5. However, because the tunneling probability is loweredin the electrons having the spins in the opposite direction to themagnetic moment of the first magnetic fixed layer 4 when the electronsis passed through the tunnel barrier layer 5, the electrons arereflected, and the electrons which are of the reflected spin electronsimpart the spin torque to the magnetic recording layer 6 again. Thereby,the magnetization direction of the magnetic recording layer 6 isdirected to the opposite direction to that of the first magnetic fixedlayer 4 (anti-parallel state).

In the spin-injection magnetization reversal method, in order toefficiently perform the magnetization reversal, the non-magnetic metallayer 7 and the second magnetic fixed layer 8 are formed by thecombination of materials in which spin reflectivity is enhanced.

In the case where the second magnetic fixed layer 8 is made of theferromagnetic material including Co (for example, Co rich), thenon-magnetic metal layer 7 is made of at least one metal selected fromthe group of Cr, Tr, Os, Ru, and Re, preferably from the group of Cr,Ir, and Os or an alloy including at least one metal thereof.

In the case where the second magnetic fixed layer 8 is made of theferromagnetic material including Fe (for example, Fe rich), thenon-magnetic metal layer 7 is made of at least one metal selected fromthe group of Mn, Cr, V, Mo, Re, Ru, Os, W, and Ti, preferably from thegroup of Mn, Cr, V, Mo, and Re or the alloy including at least one metalthereof.

In the case where the second magnetic fixed layer 8 is made of theferromagnetic material including Ni (for example, Ni rich), thenon-magnetic metal layer 7 is made of at least one metal selected fromthe group of Rh, Ru, Ir, Os, Cr, Re, W, Nb, V, Ta, and Mo, preferablyfrom the group of Rh, Ru, Ir, and Os or the alloy including at least onemetal thereof.

According to the above structure, the second magnetic fixed layer 8reflects the electron, which is spin-polarized in the opposite directionto the magnetization direction (direction of electron spin) of thesecond magnetic fixed layer 8. Therefore, the proper selection of thematerial for the non-magnetic metal layer 7 enables the efficientreflection of the electrons, spin-polarized in the opposite direction tothe magnetization direction of the second magnetic fixed layer 8, toreverse the magnetization state of the magnetic recording layer 6.

In the third embodiment, the annealing process of the first embodimentis not required because the magnetic moment directions of the firstmagnetic fixed layer 4 and the second magnetic fixed layer 8 aredirected to the same direction.

(iv) Fourth Embodiment

FIG. 14 shows a fourth embodiment of the magnetoresistive element.

The fourth embodiment is one of modifications of the third embodiment,and the fourth embodiment differs from the third embodiment in that thefirst and second magnetic fixed layers have the SAF (Syntheticanti-ferromagnetic) structures respectively.

In the fourth embodiment, the magnetoresistive element includes theanti-ferromagnetic layer 3, a first magnetic fixed layer 4SAF, thetunnel barrier layer 5, the magnetic recording layer 6, the non-magneticmetal layer 7, the second magnetic fixed layer 8SAF, and theanti-ferromagnetic layer 9. The magnetic recording layer 6 is arrangedon the first magnetic fixed layer 4SAF through tunnel barrier layer 5.The second magnetic fixed layer 8SAF is arranged on the magneticrecording layer 6 through the non-magnetic metal layer 7.

The first magnetic fixed layer 4SAF has the SAF structure, and themagnetization state of the first magnetic fixed layer 4SAF is fixed.Similarly the second magnetic fixed layer 8SAF has the SAF structure,and the magnetization state of the second magnetic fixed layer 8SAF isfixed.

In the fourth embodiment, the writing can be performed in the mannersimilar to the third embodiment.

That is, when the electrons are injected from the first magnetic fixedlayer 4 to the magnetic recording layer 6 in reversing the magneticmoments (magnetization) between the first magnetic fixed layer 4SAF andthe magnetic recording layer 6 from the anti-parallel state to theparallel state, the electrons spin-polarized in the first magnetic fixedlayer 4SAF pass through the tunnel barrier layer 5 to impart the spintorque to the magnetic recording layer 6.

The spin-polarized electrons reach the second magnetic fixed layer 8SAFfrom the magnetic recording layer 6 through the non-magnetic metal layer7. However, the spin-polarized electrons are reflected on the secondmagnetic fixed layer 8SAF, and the spin-polarized electrons, which areof the reflected spin electrons, impart the spin torque to the magneticrecording layer 6 again.

Accordingly, when the magnetic moments between the first magnetic fixedlayer 4SAF and the magnetic recording layer 6 are in the anti-parallelstate, the magnetic moment of the magnetic recording layer 6 isreversed, and the magnetic moments between the first magnetic fixedlayer 4SAF and the magnetic recording layer 6 become in the parallelstate.

When the electrons are injected from the second magnetic fixed layer8SAF to the magnetic recording layer 6 in reversing the magnetic moments(magnetization) between the first magnetic fixed layer 4 SAF and themagnetic recording layer 6 from the parallel state to the anti-parallelstate, the electrons spin-polarized in the second magnetic fixed layer8SAF pass through the non-magnetic metal layer 7 to impart the spintorque to the magnetic recording layer 6.

The spin-polarized electrons tend to flow from the magnetic recordinglayer 6 to the first magnetic fixed layer 4SAF through the tunnelbarrier layer 5. However, because the tunneling probability is loweredin the electrons having the spins in the opposite direction to themagnetic moment of the first magnetic fixed layer 4SAF when theelectrons is passed through the tunnel barrier layer 5, the electronsare reflected, and the electrons which are of the reflected spinelectrons impart the spin torque to the magnetic recording layer 6again.

Accordingly, when the magnetic moments between the first magnetic fixedlayer 4SAF and the magnetic recording layer 6 are in the parallel state,the magnetic moment of the magnetic recording layer 6 is reversed, andthe magnetic moments between the first magnetic fixed layer 4 and themagnetic recording layer 6 become in the anti-parallel state.

Thus, the magnetization reversal can be performed by changing thedirection in which the spin-injection current is passed with respect tothe magnetoresistive element, so that the writing of “0” and “1” can beperformed by the spin injection.

In the case where the first and second magnetic fixed layers 4SAF and8SAF are made of the ferromagnetic material including Co (for example,Co rich), the non-magnetic metal layer 7 is made of at least one metalselected from the group of Cr, Ir, Os, Ru, and Re, preferably from thegroup of Cr, Ir, and Os or an alloy including at least one metalthereof.

In the case where the first and second magnetic fixed layers 4SAF and8SAF are made of the ferromagnetic material including Fe (for example,Fe rich), the non-magnetic metal layer 7 is made of at least one metalselected from the group of Mn, Cr, V, Mo, Re, Ru, Os, W, and Ti,preferably from the group of Mn, Cr, V, Mo, and Re or the alloyincluding at least one metal thereof.

In the case where the first and second magnetic fixed layers 4SAF and8SAF are made of the ferromagnetic material including Ni (for example,Ni rich), the non-magnetic metal layer 7 is made of at least one metalselected from the group of Rh, Ru, Ir, Os, Cr, Re, W, Nb, V, Ta, and Mo,preferably from the group of Rh, Ru, Ir, and Os or the alloy includingat least one metal thereof.

(v) Fifth Embodiment

FIGS. 15 to 18 show a fifth embodiment of the magnetoresistive element.

The fifth embodiment is one of improvements of the first to fourthembodiments, and the fifth embodiment has the characteristic in that themagnetic recording layer is formed by plural array-shaped columnarlayers when compared with the first to fourth embodiments.

FIG. 15 is an improvement of the first embodiment shown in FIG. 11, FIG.16 is an improvement of the second embodiment shown in FIG. 12, FIG. 17is an improvement of the third embodiment shown in FIG. 13, and FIG. 18is an improvement of the fourth embodiment shown in FIG. 14.

The magnetic recording layer 6 is formed by a set of the pluralarray-shaped columnar layers (ferromagnetic body). The magnetizationdirection can be changed in each of the columnar layers. The columnarlayers are separated by insulating bodies (or dielectric bodies) 11. Thetunnel barrier layer 5 is arranged between the first magnetic fixedlayer 4 or 4SAF and the magnetic recording layer 6.

In the case of the structures shown in FIGS. 15 and 16, the non-magneticmetal layer 7 and the second magnetic fixed layer 8 or 8SAF are formedby the combination of the following materials in order to enhance thespin reflectivity.

Additionally, in the case where the second magnetic fixed layer 8 or8SAF is made of the ferromagnetic material including Co (for example, Corich), the non-magnetic metal layer 7 is made of at least one metalselected from the group of Zr, Hf, Rh, Ag, Cu, and Au, preferably fromthe group of Zr, Hf, Rh, and Ag or an alloy including at least one metalthereof.

In the case where the second magnetic fixed layer 8 or 8SAF is made ofthe ferromagnetic material including Fe (for example, Fe rich), thenon-magnetic metal layer 7 is made of at least one metal selected fromthe group of Rh, Pt, Ir, Al, Ga, Cu, and Au, preferably from the groupof Rh, Pt, Ir, Al, and Ga or the alloy including at least one metalthereof.

In the case where the second magnetic fixed layer 8 or 8SAF is made ofthe ferromagnetic material including Ni (for example, Ni rich), thenon-magnetic metal layer 7 is made of at least one metal selected fromthe group of Zr, Hf, Au, Ag, and Cu, preferably from the group of Zr,Hf, Au, and Ag or the alloy including at least one metal thereof.

In the case of the structures shown in FIGS. 17 and 18, the non-magneticmetal layer 7 and the second magnetic fixed layer 8 or 8SAF are formedby the combination of the following materials in order to enhance thespin reflectivity.

In the case where the second magnetic fixed layer 8 or 8SAF is made ofthe ferromagnetic material including Co (for example, Co rich), thenon-magnetic metal layer 7 is made of at least one metal selected fromthe group of Cr, Ir, Os, Ru, and Re, preferably from the group of Cr,Ir, and Os or an alloy including at least one metal thereof.

In the case where the second magnetic fixed layer 8 or 8SAF is made ofthe ferromagnetic material including Fe (for example, Fe rich), thenon-magnetic metal layer 7 is made of at least one metal selected fromthe group of Mn, Cr, V, Mo, Re, Ru, Os, W, and Ti, preferably from thegroup of Mn, Cr, V, Mo, and Re or the alloy including at least one metalthereof.

In the case where the second magnetic fixed layer 8 or 8SAF is made ofthe ferromagnetic material including Ni (for example, Ni rich), thenon-magnetic metal layer 7 is made of at least one metal selected fromthe group of Rh, Ru, Ir, Os, Cr, Re, W, Nb, V, Ta, and Mo, preferablyfrom the group of Rh, Ru, Ir, and Os or the alloy including at least onemetal thereof.

Thus, according to the magnetoresistive element having the magneticrecording layer 6 formed by the plural columnar layers, an effectivejunction area of the ferromagnetic tunnel junction is decreased whencompared with the first to fourth embodiments. Thereby, even if thespin-injection current is passed during the data writing, the ringmagnetic field caused by the spin-injection current is hardly generated,which allows the magnetization reversal to be stably performed in themagnetic recording layer.

The fifth embodiment is effective when the dimensions of themagnetoresistive element are relatively large. Specifically, when thecolumnar layer is formed by cylinders, it is preferable that a diameterof the columnar layer is set in the range of 1 to 100 nm.

When the diameter of the columnar layer is lower than 1 nm, theferromagnetic body of the columnar structure becomes superparamagnetism.When the diameter of the columnar layer is more than 100 nm, the stablemagnetization reversal is hardly performed due to stabilization of acirculating magnetic domain structure and the MR ratio is alsodecreased.

(vi) Summary

As described above, in the spin-injection writing method, when themagnetic recording layer 6 contains Ni—Co, Ni—Fe, Co—Fe, or Co—Fe—Ni,the non-magnetic metal layer 7 is made of at least one metal selectedfrom the group of Au, Zr, Hf, Rh, Pt, Ir, Al, and Ga or the alloyincluding at least one metal thereof. Therefore, the spin-injectioncurrent Is can be decreased.

When the magnetoresistive elements of the first to fifth embodiments areused as the memory cells of the spin-injection magnetic random accessmemory shown in FIGS. 3 to 10, the current density is decreased duringthe magnetization reversal, which allows the problems such as the tunnelbarrier layer breakage and the thermal disturbance to be solved. In thiscase, in order to stabilize the magnetization states of the first andsecond magnetic fixed layers 4 or 4SAF and 8 or 8SAF during themagnetization reversal, the volumes of the first and second magneticfixed layers 4 or 4SAF and 8 or 8SAF are enlarged as much as possible.

With reference to the SAF structure, the SAF structure can be applied toone of or both the first and second magnetic fixed layers.

(4) Writing Method

The data writing method (magnetization reversal process) with thearchitectures according to the embodiments of the invention will bedescribed below.

FIG. 19 shows a flowchart of the magnetization reversal processaccording to the embodiments of the invention. FIG. 20 shows signalwaveforms of spin-injection current and the assist magnetic field(assist current) for realizing the process of FIG. 19.

First the spin-injection current Is having the direction according tothe value of writing data is provided to the magnetoresistive element(STEP ST1, time t1). The electrons spin-polarized by the spin-injectioncurrent Is are generated, and the spin torque acts on the magneticrecording layer by the spin-polarized electrons to start themagnetization reversal.

When the spin-injection current Is is passed through themagnetoresistive element, since the temperature of the magnetoresistiveelement rises gradually (see FIG. 2), at the same timing in which thespin-injection current Ia is passes, or after the spin-injection currentIa is passes, the assist current Is is passed through the writing wordline WWL to generate the assist magnetic field H (STEP ST2, time t2).

The assist magnetic field H is generated in the magnetization easy-axisdirection of the magnetoresistive element, which suppresses the electronspin thermal disturbance in the magnetic free layer, caused by thetemperature rise of the magnetoresistive element.

The timing in which the assist current 1 a is passed through the wordline WWL to generate the assist magnetic field H may be earlier than thetiming of the passage of the spin-injection current Ia.

Then, the spin-injection current Is is cut off (STEP ST3, time t3).

In this case, as can be seen from FIG. 2, the magnetoresistive elementhas the high temperature enough to generate the electron spin thermaldisturbance until tens nanoseconds elapse since the spin-injectioncurrent Is is cut off.

Therefore, until tens nanoseconds elapse, the assist current Ta iscontinuously provided even after the spin-injection current Is is cutoff.

After the temperature of the magnetoresistive element sufficiently fallsdown, the assist current 1 a is stopped to cut off the assist magneticfield H (STEP ST4, time t4).

Thus, according to the magnetization reversal process of the embodimentsof the invention, in the current cutoff timing, since the pulse currentfor generating the assist magnetic field is later than the pulse currentfor spin-injection writing, the electron spin thermal disturbance in themagnetic recording layer caused by the temperature rise of themagnetoresistive element can effectively be prevented.

2. EXAMPLES

Then, preferred example will be described.

(1) Circuit Example

FIG. 21 schematically shows a peripheral circuit of the magnetic randomaccess memory for realizing the spin-injection magnetization reversal.

In the signs used in FIG. 21, the signs beginning with the letter “b”should mean an inversion signal in which the logic of the correspondingcompanion sign is inversed. Further, i should mean the ith row in theplural rows, and j should mean the jth column in the plural columns.

One end of the magnetoresistive element MTJ is connected to the upperbit line BLu through a contact member CNT. The other end of themagnetoresistive element MTJ is connected to the lower bit line BLdthrough the ground layer 2 which is of the lower electrode and a MOStransistor Tr which is of the selection switch. A row selection signalRWLi from the readout word line is inputted to a gate of the N-channelMOS transistor Tr.

Both the upper bit line BLu and the lower bit line BLd extend in thesame direction. That is, in the example, the upper bit line BLu and thelower bit line BLd extend in the column direction (N←→S).

One end of the upper bit line BLu is connected to a CMOS typedriver/sinker DS1. A drive signal bN2Sj is inputted to the gate of aP-channel MOS transistor constituting the driver/sinker DS1, and a syncsignal N2Sj is inputted to the gate of the N-channel MOS transistorconstituting the driver/sinker DS1.

One end of the lower bit line BLu is connected to a CMOS typedriver/sinker DS2. A drive signal bS2Nj is inputted to the gate of theP-channel MOS transistor constituting the driver/sinker DS2, and a syncsignal S2Sj is inputted to the gate of the N-channel MOS transistorconstituting the driver/sinker DS2.

For example, the row selection signal RWLi is set at “H”, the drivesignal bN2Sj and the sync signal S2Nj are set at “L”, and the drivesignal bS2Nj and the sync signal S2Nj are set at “H”, which results inthe passage of the spin-injection current Is from the driver/sinker DS1toward the driver/sinker DS2.

On the other hand, the row selection signal RWLi is set at “H”, thedrive signal bN2Sj and the sync signal S2Nj are set at “H”, and thedrive signal bS2Nj and the sync signal N2Sj are set at “L”, whichresults in the passage of the spin-injection current Is from thedriver/sinker DS2 toward the driver/sinker DS1.

The writing word line WWL extending in the row direction (E←→W) isarranged near the magnetoresistive element MTJ.

One end of the writing word line WWL is connected to a CMOS typedriver/sinker DS3. A drive signal bE2Wi is inputted to the gate of theP-channel MOS transistor constituting the driver/sinker DS3, and a syncsignal W2E1 is inputted to the gate of the N-channel MOS transistorconstituting the driver/sinker DS3.

The other end of the writing word line WWL is connected to a CMOS typedriver/sinker DS4. A drive signal bW2E1 is inputted to the gate of theP-channel MOS transistor constituting the driver/sinker DS4, and a syncsignal E2Wi is inputted to the gate of the N-channel MOS transistorconstituting the driver/sinker DS4.

For example, the drive signal bE2Wi and the sync signal E2Wi are set at“L” and the drive signal bW2E1 and the sync signal E2Wi are set at “H”,which results in the passage of the assist current Ia from thedriver/sinker DS3 toward the driver/sinker DS4.

On the other hand, the drive signal bE2W1 and the sync signal W2E1 areset at “H” and the drive signal bW2E1 and the sync signal E2Wi are setat “L”, which results in the passage of the assist current Ia from thedriver/sinker DS4 toward the driver/sinker DS3.

The other end of the upper bit line BLu is connected to a positive-sideinput terminal of a sense amplifier S/A through an N-channel MOStransistor CSW, which is of the column selection switch. The senseamplifier S/A includes, e.g., a differential amplifier. A columnselection signal CSLj is inputted to the gate of the MOS transistor CSW.

A reference potential REF is inputted to a negative-side input terminalof the sense amplifier S/A. The reference potential REF becomes areference for determining the value of the readout data from themagnetoresistive element MTJ. An output signal of the sense amplifierS/A becomes readout data ROUT of the magnetoresistive element MTJ.

(2) Signal Timing Waveform

FIG. 22 shows waveforms of the drive signal and the sync signal, whichare used for the magnetic random access memory of FIG. 21.

The signal timing waveform of FIG. 22 is one example in which thespin-injection current Is and the assist current Ia shown in FIG. 21 aregenerated.

First, at a time t1, the sync signal E2Wi is set at “H” and the drivesignal bE2Wi is set at “L”, which results in the passage of the assistcurrent Ia through the writing word line WWL from the driver/sinker DS3toward the driver/sinker DS4.

The readout selection signal RWLi is set at “H” at a time t2. Then, thesync signal N2Sj is set at “H” and the drive signal bN2Sj is set at “L”at a time t3, which results in the passage of the spin-injection currentIs from the driver/sinker DS1 toward the driver/sinker DS2.

After that, at a time t4, the sync signals N2Sj is set at “L”, the drivesignal bN2Sj is set at “H”, and the spin-injection current Is is cutoff. Then, at a time t5, the readout selection signal RWLi is set at“L”.

At a time t6 when tens nanoseconds elapse since the spin-injectioncurrent Is is cut off, the sync signal E2Wi is set at “L”, the drivesignal bE2Wi is set at “H”, the assist current Ia is cut off, and theassist magnetic field H is eliminated.

In the signal timing waveform of the example, the assist current Ia ispassed to generate the assist magnetic field H prior to the passage ofthe spin-injection current Is. However, as described above, the assistmagnetic field H may be generated at the same time of the passage of thespin-injection current Is or after the passage of the spin-injectioncurrent Is.

(3) Decoder

Examples of a decoder, which controls the control the driver/sinkersDS1, DS2, DS3, and DS4 of FIG. 21 will be described below.

During the data writing in the magnetoresistive element, the decodercontrols the driver/sinker to determine the directions of thespin-injection current Is and the assist current Ia according to thevalue of the writing data. The decoder also controls the driver/sinkerto determine the timing of the supply/cutoff of the spin-injectioncurrent Is and the assist current Ia.

FIG. 23 shows an example of the decoder, which generates the readoutselection signal RWLi.

In this example, the decoder includes an AND gate circuit. The readoutselection signal RWLi becomes “H” when both an active signal RWL and arow address signal are set in “H”.

FIG. 24 shows an example of the decoder, which generates the drivesignals bE2Wi and the sync signal E2Wi.

In this example, the decoder includes the AND gate circuit. The drivesignal bE2Wi becomes “L” and the sync signal E2Wi becomes “H”, when bothan active signal E2W and a row address signal are set in “H”.

FIG. 25 shows an example of the decoder, which generates the drivesignals bW2E1 and the sync signal W2E1.

In this example, the decoder includes the AND gate circuit. The drivesignals bW2E1 and the sync signal W2E1 become “H”, when both an activesignal W2E and the row address signal are set in “H”.

FIG. 26 shows an example of the decoder which generates the drivesignals bN2Sj and the sync signal N2Sj.

In this example, the decoder includes the AND gate circuit. The drivesignal bN2Sj becomes “L” and the sync signal N2Sj becomes “H”, when bothan active signal N2S and a column address signal are set in “H”.

FIG. 27 shows an example of the decoder, which generates the drivesignals bS2Nj and the sync signal S2Nj.

In this example, the decoder includes the AND gate circuit. The drivesignal bS2Nj becomes “L” and the sync signal S2Nj becomes “H”, when bothan active signal S2N and the column address signal are set in “H”.

FIGS. 28 to 32 show circuits, which generate the active signals RWL,E2W, W2E, N2S, and S2N.

Signals A, B, C, D, E and F determine the timing in which the signalsRWL, E2W, W2E, N2S, and S2N are outputted respectively.

In FIGS. 29 to 32, DATA1 is the signal which becomes “H” when thewriting data is “1” and DATA0 is the signal which becomes “H” when thewriting data is “0”.

Accordingly, the directions of the spin-injection current Is and theassist current Ia are determined according to the value of the writingdata.

In the examples, the timing of the passage of the assist current Ia isset before the passage of the spin-injection current Is. However, thetiming of the passage of the assist current Ia may be set at the sametime of the passage of the spin-injection current Is or after thepassage of the spin-injection current Is.

FIGS. 33 and 34 show delay circuits 1 to 6, which generate the signalsA, B, C, D, E, and F. based on a writing signal WRITE.

FIG. 35 shows operation waveforms of the delay circuits 1 to 6 of FIGS.33 and 34.

FIGS. 36 and 37 show examples of the delay circuits 1 to 6.

The example of FIG. 36 is an inverter type in which the delay circuit isformed by the plural inverters connected in series. The delay time canbe controlled by the number of inverters. The example of FIG. 37 is anRC type in which the delay circuit is formed by a resistor R and acapacitance C. The delay time can be controlled by a resistance value ofthe resistor R and a capacitance value of the capacitance C.

3. MODIFICATIONS

Modifications of the structure (see FIGS. 3 to 10) according to theembodiments of the invention will be described below.

(1) First Modification

FIGS. 38 to 45 show the modifications of the structure according to theembodiments of the invention.

The modifications have the so-called yoke wiring structure in which amagnetic layer 12 made of a soft magnetic material (yoke material) isarranged around the writing word line WWL in order to efficiently impartthe assist magnetic field H to the magnetoresistive element MTJ.

According to the yoke wiring structure, the assist current Ia forgenerating the assist magnetic field H can be further decreased.Specifically the assist current Ia can be set at values not more than0.5 mA.

The structures shown in FIGS. 38 to 45 correspond to the structuresshown in FIGS. 3 to 10 respectively.

(2) Second Modification

With reference to the magnetoresistive element, the followingmodifications can be performed.

In the magnetoresistive elements shown in FIGS. 11 to 18, theanti-ferromagnetic layer 3 or 9 can be made of the materials such asFe—Mn, Pt—Mn, Pt—Cr—Mn, Ni—Mn, Ir—Mn, NiO, and Fe₂O₃.

The first and second magnetic fixed layers 4 or 4SAF and 8 or 8SAF canbe made of the material having unidirectional anisotropy, and themagnetic recording layer 6 can be made of the material having uniaxialanisotropy. The thicknesses of the ferromagnetic layers constituting thefirst second magnetic fixed layers 4 or 4SAF and 8 or 8SAF and themagnetic recording layer 6 are set in the range of 0.1 nm to 100 nm. Inorder to ensure that the ferromagnetic body is not changed to thesuperparamagnetic body, it is preferable that the thicknesses of theferromagnetic layers are not lower than 0.4 nm.

In the magnetoresistive elements shown in FIGS. 15 to 18, the columnarlayer, which is of the ferromagnetic particles partitioned by thedielectric body can be made of Co, Fe, or Ni or the alloy thereof, or atleast one metal selected from the group of Co—Pt, Co—Fe—Pt, Fe—Pt,Co—Fe—Cr—Pt, and Co—Cr—Pt.

In the magnetic recording layer 6 of the magnetoresistive element shownin FIGS. 11 to 18, physical properties such as the magnetic properties,the crystallinity, the mechanical properties, and the chemicalproperties can be adjusted by adding the non-magnetic elements such asAg, Cu, Au, Al, Ru, Os, Re, Ta, B, C, O, N, Pd, Pt, Zr, Ir, W, Mo, andNb to the magnetic material.

4. EXPERIMENTAL EXAMPLE

Then, experimental examples will be described.

(1) First Experimental Example

A first experimental example is a spin-injection magnetic random accessmemory, which includes the structure of FIG. 6 and the circuits of FIGS.21 to 37.

The magnetoresistive element whose magnetic fixed layer has the SAFstructure shown in FIG. 12 or 14 is used as the magnetoresistive elementof the first experimental example.

The procedure of producing the first experimental example is as follows:

First the MOS transistors and the writing word lines WWL are formed onthe semiconductor substrate. Then, the magnetoresistive element whosemagnetic fixed layer has the SAF structure shown in FIG. 12 or 14 isformed.

In the case of the magnetoresistive element (sample 1 a) of FIG. 12,lamination of Ta/Cu/Ta is formed as the ground layer (electrode layer)2.

The anti-ferromagnetic layer 3 made of Ru (5 nm)/PtMn (20 nm) is formedon the ground layer 2. The first magnetic fixed layer 4 made of CO₇₅Fe₂₅(5 nm), the tunnel barrier layer 5 made of AlO_(X) (1.4 nm), and themagnetic recording layer 6 made of Co₉₀Fe₁₀ (3 nm) are sequentiallyformed on the anti-ferromagnetic layer 3.

The non-magnetic metal layer 7 made of Cu (5 nm) is formed on themagnetic recording layer 6. The second magnetic fixed layer 8SAF made ofCO₇₅Fe₂₅ (5 nm)/Ru (0.9 nm)/CO₇₅Fe₂₅ (5 nm) is formed on thenon-magnetic metal layer 7. The anti-ferromagnetic layer 9 made of PtMn(20 nm)/Ru (5 nm) is formed on the second magnetic fixed layer 8SAF.

Then, the electrode layer 10 made of Ta (150 nm) is formed on theanti-ferromagnetic layer 9.

In the case of the magnetoresistive element (sample 1 b) of FIG. 14, thelamination of Ta/Cu/Ta is formed as the ground layer (electrode layer)2.

The anti-ferromagnetic layer 3 made of Ru (5 nm)/PtMn (20 nm) is formedon the ground layer 2. The first magnetic fixed layer 4SAF made ofCO₇₅Fe₂₅ (5 nm)/Ru (0.9 nm)/CO₇₅Fe₂₅ (5 nm) is formed on theanti-ferromagnetic layer 3. The tunnel barrier layer 5 made of AlO_(X)(1.4 nm) and the magnetic recording layer 6 made of Co₉₀Fe₁₀ (3 nm) aresequentially formed on the first magnetic fixed layer 4SAF.

The non-magnetic metal layer 7 made of Cu (5 nm) is formed on themagnetic recording layer 6. The second magnetic fixed layer 8SAF made ofCO₇₅Fe₂₅ (5 nm)/Ru (0.9 nm)/CO₇₅Fe₂₅ (5 nm) is formed on thenon-magnetic metal layer 7. The anti-ferromagnetic layer 9 made of PtMn(20 nm)/Ru (5 nm) is formed on the second magnetic fixed layer 8SAF.

Then, the electrode layer 10 made of Ta (150 nm) is formed on theanti-ferromagnetic layer 9.

At this point, for example, after Al having the thickness of 0.6 nm isformed, the tunnel barrier layer 5 made of AlO_(X) having the thicknessof 1.4 nm can be produced by repeating the process twice in which Al isnaturally oxidized in situ with pure oxygen.

The cross-sectional observation of the thickness of AlO_(X) producedthrough the above processes with TEM (Transmission Electron Microscope)confirms that the thickness of AlO_(X) becomes 1.4 nm due to theoxidation while the total thickness of Al layers is 1.2(=0.6+0.6) nm.

The tunnel junction in the portion, which defines the junction area canbe formed with an EB (Electron Beam) imaging apparatus, and the tunneljunction in other portions can be formed with KrF stepper apparatus. Thejunction area is 0.1×0.15 μm2.

After junction isolation is performed, a protection made of SiO_(X)whose thickness is 35 nm is formed, and the electrode made of Ta/Ru isformed. Then, after a contact layer is exposed by etch back, contactcleaning is performed to formed the upper electrode made of Ti (15nm)/Al (300 nm)/Ti (15 nm). Then, the annealing is performed to impartthe uniaxial anisotropy to the magnetoresistive element at 280° C. for10 hours while the magnetic field is applied in the major axis of themagnetic layer.

FIG. 46 shows thermal disturbance of the magnetoresistive element(sample 1 a) according to the first experimental example, and FIG. 47shows thermal disturbance of the magnetoresistive element (sample 1 b)according to the first experimental example.

When the results shown in FIGS. 46 and 47 are obtained, in order to makeclear the difference in effect between the prior art (FIG. 1) and theinvention, the same conditions as that in the prior art aresubstantially adopted. This is, the spin-injection writing time is setat 50 ns, the assist current is set at 0.4 mA, and the delay timebetween the cutoff of the spin-injection current and the cutoff of theassist current is set at 20 ns.

As can be seen from these drawings, in the samples 1 a and 1 b of thefirst experimental example, the fluctuation in current density of thepulse current (corresponding to pulse voltage) and the fluctuation inmagnetoresistance fluctuation rate (corresponding to junctionresistance) of the post-switching are largely decreased. In themagnetization reversal (switching), it is necessary to decrease thefluctuation in current density of the pulse current and the fluctuationin magnetoresistance fluctuation rate of the post-switching.

These results can be obtained in a same manner, regardless of the timingof the assist magnetic field generation, i.e., the timing of the assistmagnetic field generation is independent of the timing of thespin-injection current passage. Therefore, the results can contribute tothe practical use of the large-capacity magnetic random access memory.

(2) Second Experimental Example

A second experimental example is a spin-injection magnetic random accessmemory, which includes the structure of FIG. 41 and the circuits ofFIGS. 21 to 37.

The magnetoresistive element whose magnetic fixed layer has the SAFstructure shown in FIG. 12 or 14 is used as the magnetoresistive elementof the first experimental example.

The procedure of producing the first experimental example is as follows:

First the MOS transistors and the writing word lines WWL having the yokestructure are formed on the semiconductor substrate. Then, themagnetoresistive element whose magnetic fixed layer has the SAFstructure shown in FIG. 12 or 14 is formed.

In the case of the magnetoresistive element (sample 2 a) of FIG. 12, forexample, the lamination of Ta/Cu/Ta is formed as the ground layer(electrode layer) 2.

The anti-ferromagnetic layer 3 made of Ru (5 nm)/PtMn (20 nm) is formedon the ground layer 2. The first magnetic fixed layer 4 made of CO₆₅Fe₃₅(5 nm), the tunnel barrier layer 5 made of MgO (0.9 nm), and themagnetic recording layer 6 made of (CO₆₅Fe₃₅)₈₀B₂₀ (3.5 nm) aresequentially formed on the anti-ferromagnetic layer 3.

The non-magnetic metal layer 7 made of Rh (5 nm) is formed on themagnetic recording layer 6. The second magnetic fixed layer 8SAF made ofCO₇₅Fe₂₅ (5 nm)/Ru (0.9 nm)/CO₇₅Fe₂₅ (5 nm) is formed on thenon-magnetic metal layer 7. The anti-ferromagnetic layer 9 made of PtMn(20 nm)/Ru (5 nm) is formed on the second magnetic fixed layer 8SAF.

Then, the electrode layer 10 made of Ta (150 nm) is formed on theanti-ferromagnetic layer 9.

In the case of the magnetoresistive element (sample 2 b) of FIG. 14, forexample, the lamination of Ta/Cu/Ta is formed as the ground layer(electrode layer) 2.

The anti-ferromagnetic layer 3 made of Ru (5 nm)/PtMn (20 nm) is formedon the ground layer 2. The first magnetic fixed layer 4SAF made ofCO₇₅Fe₂₅ (5 nm)/Ru (0.9 nm)/CO₇₅Fe₂₅ (5 nm) is formed on theanti-ferromagnetic layer 3. The tunnel barrier layer 5 made of MgO (0.9nm) and the magnetic recording layer 6 made of (CO₆₅Fe₃₅)₈₀B₂₀ (3.5 mm)are sequentially formed on the first magnetic fixed layer 4SAF.

The non-magnetic metal layer 7 made of Rh (5 nm) is formed on themagnetic recording layer 6. The second magnetic fixed layer 8SAF made ofCO₇₅Fe₂₅ (5 nm)/Ru (0.9 nm)/CO₇₅Fe₂₅ (5 nm) is formed on thenon-magnetic metal layer 7. The anti-ferromagnetic layer 9 made of PtMn(20 nm)/Ru (5 nm) is formed on the second magnetic fixed layer 8SAF.

Then, the electrode layer 10 made of Ta (150 nm) is formed on theanti-ferromagnetic layer 9.

At this point, for example, after Mg can be formed by RF directsputtering, the tunnel barrier layer 5 made of MgO having the thickness0.9 nm can be produced by performing plasma oxidation for 3 seconds.

The uniaxial anisotropy of the magnetoresistive element can be impartedin the same way as the first experimental example.

FIG. 48 shows thermal disturbance of the magnetoresistive element(sample 2 a) according to the second experimental example, and FIG. 49shows thermal disturbance of the magnetoresistive element (sample 2 b)according to the second experimental example.

When the results shown in FIGS. 48 and 49 are obtained, in order to makeclear the difference in effects between the prior art (FIG. 1) and theinvention, the same conditions as the prior art are substantiallyadopted. This is, the spin-injection writing time is set at 50 ns, theassist current is set at 0.2 mA, and the delay time between the cutoffof the spin-injection current and the cutoff of the assist current isset at 20 ns.

As can be seen from these drawings, in the samples 2 a and 2 b of thesecond experimental example, the fluctuation in current density of thepulse current (corresponding to pulse voltage) and the fluctuation inmagnetoresistance fluctuation rate (corresponding to junctionresistance) of the post-switching are largely decreased. In themagnetization reversal (switching), it is necessary to decrease thefluctuation in current density of the pulse current and the fluctuationin magnetoresistance fluctuation rate of the post-switching.

These results can be obtained in a same manner regardless of the timingof the assist magnetic field generation, i.e., the timing of the assistmagnetic field generation is independent of the timing of thespin-injection current passage. Therefore, the results can contribute tothe practical use of the large-capacity magnetic random access memory.

5. OTHER

As described above, according to the invention, in the spin-injectionmagnetic random access memory, the problems such as the tunnel barrierbreakage and the thermal disturbance caused by the temperature rise ofthe magnetoresistive element can be solved by the new architecture andwriting method.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A random access memory with a magnetoresistive element, comprising: amemory cell including a MOS transistor and a magnetoresistive elementhaving a magnetic fixed layer whose magnetization direction is fixed, amagnetic recording layer whose magnetization direction can be changed byinjecting spin-polarized electrons, and a tunnel barrier layer which isprovided between the magnetic fixed layer and the magnetic recordinglayer; a bit line which passes a first current through themagnetoresistive element, the first current being used for generation ofa spin-polarized electrons; a word line through which a second currentis passed, the second current being used for the generation of an assistmagnetic field in a magnetization easy-axis direction of themagnetoresistive element; a first driver connected to the bit line andsupplies the first current; a second driver connected to the word lineand supplies the second current; a first decoder which receives awriting data to be written into the magnetoresistive element andcontrols the first driver to determine a direction of the first currentdepending on the writing data, and determines timing of cutoff of thefirst current; and a second decoder which controls the second driver todetermine the direction of the second current depending on the writingdata, and makes the timing of the cutoff of the second current laterthan the timing of the cutoff of the first current.
 2. The memoryaccording to claim 1, wherein the bit line and the writing word lineintersect each other.
 3. The memory according to claim 1, wherein thebit line and the writing word line extend in parallel with each other.4. The memory according to claim 1, wherein the second current is cutoff at a time when at least 50 nanoseconds elapse since the firstcurrent is cut off.
 5. The memory according to claim 1, wherein thesecond current is not more than 1 mA.
 6. The memory according to claim1, wherein the magnetoresistive element has an another magnetic fixedlayer located on a side of the magnetic recording layer which isopposite the tunnel barrier layer, the another magnetic fixed layerhaving magnetization fixed in an opposite direction to the magnetizationdirection of the magnetic fixed layer.
 7. The memory according to claim1, wherein the magnetoresistive element has an another magnetic fixedlayer located on a side of the magnetic recording layer which isopposite the tunnel barrier layer, the another magnetic fixed layerhaving magnetization fixed in a same direction as the magnetizationdirection of the magnetic fixed layer.
 8. The memory according to claim1, wherein the magnetic recording layer is formed by a plurality ofcolumnar layers which are partitioned by insulating bodies or dielectricbodies.
 9. The memory according to claim 1, wherein the writing wordline has a yoke wiring structure.
 10. The memory according to claim 1,wherein the magnetoresistive element is arranged above a semiconductorsubstrate and the writing word line is arranged between themagnetoresistive element and the semiconductor substrate.
 11. The memoryaccording to claim 1, wherein the magnetoresistive element is arrangedabove a semiconductor substrate and the writing word line is arrangedabove the magnetoresistive element.
 12. The memory according to claim 1,wherein one end of the magnetoresistive element is connected to the bitline and another end is connected to the MOS transistor.